Factors affecting Vmc
08-14-2007, 01:26 PM
#12
Gets Weekends Off
Joined APC: Oct 2006
Position: ERJ
Posts: 211
Originally Posted by exerauflyboy5
Since I'm currently stuck in Las Vegas at ATP's CFI’s school and I’ve been over this more times than I can count. All I can add is this,
SMACFUM- The conditions that affect VMC,
Sea level pressure-increases VMC
Max power on the operating engine-Increases VMC
Aft legal C.G-Increases VMC
Critical engine Wind milling-Increases VMC
Flaps/gear down-decreases VMC
Up to 5 degrees of bank into operating engine-Decreases VMC
Most unfavorable weight-A lighter airplane has a higher VMC than heavier airplane
YUM-YUM
SMACFUM- The conditions that affect VMC,
Sea level pressure-increases VMC
Max power on the operating engine-Increases VMC
Aft legal C.G-Increases VMC
Critical engine Wind milling-Increases VMC
Flaps/gear down-decreases VMC
Up to 5 degrees of bank into operating engine-Decreases VMC
Most unfavorable weight-A lighter airplane has a higher VMC than heavier airplane
YUM-YUM
08-14-2007, 09:31 PM
#14
Line Holder
Joined APC: May 2007
Position: MeSAABa
Posts: 79
All factors related to Vmc have to do with rudder authority. Think through all of the various factors in terms of whether rudder authority increases or decreases. Increased rudder authority = a decrease in Vmc.
Any conversation regarding Vmc should start with a conversation of the definition of Vmc. What is Vmc? The speed at which you loose directional control of the aircraft. In other words you loose rudder authority. So you must believe that the rudder is the primary flight control for heading. If you are out of rudder... you have lost directional control. Whenyou loose directional control, then you Vmc.
How dangerous is Vmc? Or perhaps this should be framed as, "What is more dangerous, the stall or the Vmc?" For all the conversation that we have in multiengine training regarding the dangers of Vmc it is the stall that is the most dangerous. You can Vmc the airplane all day long... but don't stall. (Problem is that you are probably going to stall just before you Vmc in say... a Seminole.) Look carefully at the graph that shows stall speed and the curved line of Vmc; move the Vmc line back and forth as you apply the increasing and decreasing factors that affect Vmc.
As an aside, be sure to make a clear distinction in your head between the factors that affect Vmc and the four factors that make the left engine critical.
Any conversation regarding Vmc should start with a conversation of the definition of Vmc. What is Vmc? The speed at which you loose directional control of the aircraft. In other words you loose rudder authority. So you must believe that the rudder is the primary flight control for heading. If you are out of rudder... you have lost directional control. Whenyou loose directional control, then you Vmc.
How dangerous is Vmc? Or perhaps this should be framed as, "What is more dangerous, the stall or the Vmc?" For all the conversation that we have in multiengine training regarding the dangers of Vmc it is the stall that is the most dangerous. You can Vmc the airplane all day long... but don't stall. (Problem is that you are probably going to stall just before you Vmc in say... a Seminole.) Look carefully at the graph that shows stall speed and the curved line of Vmc; move the Vmc line back and forth as you apply the increasing and decreasing factors that affect Vmc.
As an aside, be sure to make a clear distinction in your head between the factors that affect Vmc and the four factors that make the left engine critical.
08-15-2007, 11:15 AM
#15
On a beach with no ocean
Joined APC: Aug 2006
Position: Unmanned
Posts: 166
Frank
Out here in ATP land las vegas, there is a ground school instructor named frank varsalona. He is a very animated person, and uses the term YUM-YUM to describe alot of things. And when he talks about flying his mooooooneeeee, he makes a cat like noise and goes MEEEEOOOOWWWWWW while using a flying motion with his hand. Unfortunately i did not get his sign off 
and now im on my way back to cali to look at my options. I was here for 3 weeks, drew JIM DIAGLE as a check pilot, and got a unanimous, "your F'ed", for all the CFI's, then i got sick and the rest is mentioned above. As far as im concerned, ATP can take this training and shove it!!!
and now im on my way back to cali to look at my options. I was here for 3 weeks, drew JIM DIAGLE as a check pilot, and got a unanimous, "your F'ed", for all the CFI's, then i got sick and the rest is mentioned above. As far as im concerned, ATP can take this training and shove it!!!
08-17-2007, 06:11 AM
#16
Moderator
Joined APC: May 2006
Position: ATP, CFI etc.
Posts: 6,056
ATP takes a fair amount of risk when it accepts a student. If you screw up on your checkride the CFI gets a bad mark out of it too. Enough of those, and they are not a CFI anymore. And as all CFIs know, the job doesn't pay very much.
01-20-2011, 08:29 AM
#17
On Reserve
Joined APC: Jan 2011
Position: Jet SIC
Posts: 20
11 factors
There are actually 11 factors now. At least this is what I was taught last month. (I am currently doing Mutli-Engine training in a Seminole) My instructor mentioned to list them as in order of flight preparation and occurrence, like you are doing a preflight plan and then you pretakeoff and then takeoff then cruise
1. Weight (Unfavorable=Light)
2. CG (Unfaborable=Aft)
3. Density Alt=0
4. Trim: set for Takeoff
5. Flaps: set for Takeoff
6. Cowl Flaps: set for Takeoff
7. Propeller [Critical Eng] windmilling
8. Max available takeoff power op. eng
9. Gear up (This is unfavorable: no keel effect)
10. Out of Ground Effect
11. Max of a 5degree bank towards op eng
Know how each affects the controlability and theperformance.
These are the items which each multi airplane is certified with by the FAA standards when calculating it's Vmc.
Hope it helps!
1. Weight (Unfavorable=Light)
2. CG (Unfaborable=Aft)
3. Density Alt=0
4. Trim: set for Takeoff
5. Flaps: set for Takeoff
6. Cowl Flaps: set for Takeoff
7. Propeller [Critical Eng] windmilling
8. Max available takeoff power op. eng
9. Gear up (This is unfavorable: no keel effect)
10. Out of Ground Effect
11. Max of a 5degree bank towards op eng
Know how each affects the controlability and theperformance.
These are the items which each multi airplane is certified with by the FAA standards when calculating it's Vmc.
Hope it helps!
01-20-2011, 09:09 AM
#18
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Position: ATP, CFI etc.
Posts: 6,056
Thanks Ace & welcome to APC. This thread is bit out of date now although the topic never is.
Item 10 looks new. Who is including that, AllATPs? I will have to think about how drag reduction at the wing would affect one side more than the other. One thing to remember is the low-speed (ie. vmc) regime is one where the drag curve goes up exponentially with decrease in speed. So there is a lot of induced drag to begin with, and any change due to ground effect will receive an amplified effect. Ground effect would greatly reduce drag and it would affect the wings unequally since the wings are loaded unequally. That would be my theory anyway.
Item 10 looks new. Who is including that, AllATPs? I will have to think about how drag reduction at the wing would affect one side more than the other. One thing to remember is the low-speed (ie. vmc) regime is one where the drag curve goes up exponentially with decrease in speed. So there is a lot of induced drag to begin with, and any change due to ground effect will receive an amplified effect. Ground effect would greatly reduce drag and it would affect the wings unequally since the wings are loaded unequally. That would be my theory anyway.
Last edited by Cubdriver; 01-20-2011 at 09:20 AM.
01-20-2011, 04:53 PM
#19
On Reserve
Joined APC: Jul 2010
Position: International Charter Pilot, Citation V
Posts: 13
Oh wow, I can't believe I'm going to type this but here goes, hope it helps
CRM LOFT ACE
C - Critical engine inop and windmilling (windmilling drag is significant compared to feathered)
R - Most rearward CG (rudder effective arm is reduced)
M - Most unfavorable weight (light weight. Remember your horizontal component of lift and how it opposes your operating engine)
L - Landing gear (as required by manufacturer certification)
O - Operating engine at max takeoff power (and remember this can only occur at sea level in standard conditions
F - Flaps (again as required by manufacturer certification
T- Trim for takeoff (an aircraft not trim for takeoff will require control loads outside of those necessary. Especially in the case of a rudder trim which is an anti-servo tab style.)
A - Airborne and out of ground effect (remember the effect that better performance can have when close to the ground)
C - Cowl Flaps (as required again by manufacturer setting. Especially for those flying a seminole this is required to be open)
E - Eliminate sideslip (max 5 degrees towards good engine)
If you really need more theory explanation behind some of these I would be more than happy to help. I've got a few thousand hours of dual given behind me and I am more than happy to point you at some resources as well.
CRM LOFT ACE
C - Critical engine inop and windmilling (windmilling drag is significant compared to feathered)
R - Most rearward CG (rudder effective arm is reduced)
M - Most unfavorable weight (light weight. Remember your horizontal component of lift and how it opposes your operating engine)
L - Landing gear (as required by manufacturer certification)
O - Operating engine at max takeoff power (and remember this can only occur at sea level in standard conditions
F - Flaps (again as required by manufacturer certification
T- Trim for takeoff (an aircraft not trim for takeoff will require control loads outside of those necessary. Especially in the case of a rudder trim which is an anti-servo tab style.)
A - Airborne and out of ground effect (remember the effect that better performance can have when close to the ground)
C - Cowl Flaps (as required again by manufacturer setting. Especially for those flying a seminole this is required to be open)
E - Eliminate sideslip (max 5 degrees towards good engine)
If you really need more theory explanation behind some of these I would be more than happy to help. I've got a few thousand hours of dual given behind me and I am more than happy to point you at some resources as well.
01-20-2011, 05:02 PM
#20
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Joined APC: May 2006
Position: ATP, CFI etc.
Posts: 6,056
Out of ground effect would help explain why a conventional twin with a dead engine has a tendency to roll over and dive into the ground only after it gets about a hundred feet up. It could also just be decay of airspeed as the airplane pitches up trying to clear an obstacle.
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